The effect and site of action of indoleamines on the hypothalamic centers involved in the control of LH release and ovulation in sheep.

Serotonin or melatonin was infused into the 3rd cerebral ventricle (3rd V) or into the medial basal hypothalamus (MBH) of both intact ewes and ewes with lesions of the anterior hypothalamic area (AHA). Prolongation of the estrous cycle and delay of ovulation were obtained after infusions of melatonin or serotonin in both the intact and lesioned ewes. Statistically, serotonin proved to be more effective in this respect than melatonin in the intact ewes. The infusions also blocked the prevulatory peak of LH. Furthermore, the infusion of serotonin blocked estrous behavior, while that of melatonin did not affect this function. The effect of indoleamine infusions in the lesioned ewes, in which the inhibitory action of the AHA over the transmission of gonadotrophic releasing hormones (G-RH) had been eliminated, seems to indicate that the inhibitory action of indoleamines on the release of these neurohormones is being displayed at the level of the MBH.